Near Field Communication or NFC, is a short-range high frequency wireless communication technology which enables the exchange of data between devices over about a decimeter distance. The technology is an extension of the ISO 14443 proximity-card standard (contactless card, RFID) that combines the interface of a smartcard and a reader into a single device. NFC is an open platform technology standardized in ECMA-340 and ISO 18092. An NFC device can communicate with both existing ISO 14443 smartcards and readers, as well as with other NFC devices, and is thereby compatible with existing contactless infrastructure already in use for e.g. public transportation and payment. Presently, NFC is primarily aimed at usage in mobile phones.
NFC devices communicate with each other via magnetic field induction, where each of the NFC device comprises a loop antenna. The two antennas are located within each other's near field, effectively forming an air-core transformer. NFC devices operate within a frequency band of 13.56 MHz, with a bandwidth of almost 2 MHz.
There are two operating modes provided:
Passive Communication Mode: In this mode an NFC connection is built from an “initiator” to a “target”. The initiator thereby acts as an active device, constantly emitting an electromagnetic carrier signal field. The target is inactive (from an energetic point of view), i.e. it does not emit a radio field. The initiator transmits data to the target by modulating its carrier signal during a data transmission (e.g. by on/off keying). Data transmission from the target to the initiator occurs in that the target modulates the existing electromagnetic carrier signal field by means of load modulation. Load modulation means that the target changes the resistance of a circuit which comprises a receiving coil that receives the carrier signal. This change of electric resistance can be accomplished by adding and removing resistors or by short-circuiting of the receiving coil and causes a detectable voltage drop in a transmitting coil of the initiator, since receiving coil and transmitting coil act as primary and secondary coils of a transformer coupled via an air-core. By means of sequences of changing the electrical resistance data are serially transmitted from the target to the initiator. In this mode, the target device may draw its operating power from the initiator-provided electromagnetic field, thus making the target device a transponder.
Active Communication Mode: Both initiator and target device communicate by alternately generating their own modulated electromagnetic fields. A device deactivates its RF field while it is waiting for data. In this mode, both devices typically need to have a power supply. In this active communication mode the prevailing modulation processes are Manchester coding and Modified Miller coding.
While NFC has proved to be a reliable data transmission system it suffers from the drawback that the achievable data transmission rates are limited (typically data transmission rates of less than 500 kBd are achieved).
The problem of insufficient data transmission rates generally applies to Radio Frequency Identification (RFID) systems and hinders the implementation of highly-developed RFID applications. An example of such an application is an electronic passport where photographs, fingerprints and other biometric data are stored in an RF transponder and have to be transferred to a reader within the shortest time possible in order to avoid long queues at immigration lines or the like.
While date transmission rates could be raised by enlarging the bandwidth this simple approach is not feasible since the available bandwidths are strictly regulated by international standards and there are no free frequency bands. Hitherto, the only way to steer out of this dead end seemed to make use of higher order modulation schemes which suffer from the drawback that their implementation is rather complex and requires high technical efforts.